The present invention relates to a fluid exhausting device such as, typically, an air exhausting unit of a portable vacuum cleaner for removing dust and dirt from floors, walls, furniture, upholstery or other surfaces by air suction.
An air exhausting unit of a portable vacuum cleaner for household or office use or for use in an automotive vehicle is ordinarily of the type which comprises a centrifugal fan including a motor-driven rotor formed with a central opening having a center axis coincident with the axis of rotation of the rotor and a number of rotor blades extending radially outwardly from the central opening. The rotor is enclosed within a coaxial rotor housing which has an annular front wall portion formed with an air inlet opening located immediately upstream of the central opening in the rotor and a cylindrical side wall portion which defines an annular passageway encircling the rotor for collecting the air delivered from the rotor. The rotor is driven for rotation about its axis by an electric motor which is positioned on the leeward side of the rotor. The motor is enclosed within a motor housing which is fixedly secured to the rotor housing so that a generally cylindrical air outlet passageway in constant communication with the annular passageway in the rotor housing is provided around the motor. Between the annular passageway in the rotor housing and the cylindrical passageway in the motor housing are located a plurality of stationary outlet guide vanes which are arranged to establish spiral flows of air at the entrance to the cylindrical air outlet passageway. The flow of air in the motor housing is discharged to the atmosphere usually from the rear end of the outlet passageway.
In an air exhausting device of the above described construction, the flows of air past the outlet guide vanes are subjected to no compulsive spinning actions in the absence of guide means downstream of the vanes and, as a consequence, turbulence is produced in the outlet passageway in the motor housing by the externally projecting parts of the motor disrupting the stream of air through the passageway. The turbulent flows thus induced on the leeward side of the fan are not only the important cause of noises but tend to reduce the horsepower taken by the fan and will deteriorate the performance efficiency of the fan.